1. Field of the Invention
The present invention relates to an organic electroluminescent display device (organic EL display device) and, more particularly, to an organic EL display device having an improved organic EL element encapsulating structure.
2. Description of the Related Art
An organic EL element incorporated into an organic EL display device generally has a transparent anode formed on an array substrate, a lattice-like bank formed on this anode to define a plurality of pixel regions, hole transporting layers formed on the anode exposed to these pixel regions, light emitting layers formed on these hole transporting layers so as to be lower than the upper surface of the bank, and made of an organic compound, and a cathode formed on the bank including these light emitting layers.
When this organic EL element is left to stand in the atmosphere, the atmospheric water and oxygen degrade the light emitting layers and cathode, and this degrades the performance of the element. More specifically, a non-light-emitting region called a dark spot is formed, and this dark spot expands with time.
To prevent this, organic EL display devices having various encapsulating structures for protecting the organic EL element from the outside have been researched and developed.
Examples of known techniques are a technique by which an organic EL element is covered and encapsulated with a moisture-resistant layer which is a laminated film obtained by stacking silicon oxide on a polyethyleneterephthalate film, and a technique by which an organic EL element is covered and encapsulated with an organic insulating layer containing silicon oxide or silicon nitride.
Unfortunately, when the moisture-resistant layer made of a laminated film is used, it is difficult to effectively prevent organic EL element degradation caused by water.
Also, when an organic EL element is encapsulated only with the inorganic insulating layer, the productivity lowers or the wear resistance lowers in order to increase the thickness.
Jpn. Pat. Appln. KOKAI Publication No. 2002-056971 describes a method in which a glass, plastic, or metal encapsulating can is filled with a gas such as nitrogen containing barium oxide having a moisture absorbing effect, or with an inert liquid having little influence on an organic EL element, thereby forming an encapsulating layer. However, these encapsulating structures have problems that heat generated when the organic EL display device is driven cannot be well dissipated, i.e., the heat dissipation properties degrade, and the thickness of the organic EL display device itself increases.
It is an object of the present invention to provide an organic EL display device which improves the reliability and durability by suppressing deterioration of an organic EL element for long time periods by stopping external water penetration.